Cranking no spark

[RonD]

That's the screwdriver and stopwatch test. Zap yourself and time how long until you can feel your arm again.

I thought that was the weak(yellow) or strong(blue) spark test

 

[adsm08]

I thought that was the weak(yellow) or strong(blue) spark test

Well, that depends on exactly how grounded you are to the vehicle.

 

[dcpppf]

depends on OHM meter but 0.5 to 0.8 would be expected, under 0.4 seems too low
Take your meter with you to the parts store and test the new one to see

There is no test for a "good" coil, you can only test for a "bad" coil, and not showing its a bad coil doesn't mean its a good coil, lol

^ this is good to know for sure, and will keep that in the back of my mind.

However, good news (i think). Took the TFI module to O'reilly's to get tested... I was expecting it to pass and I'd pick up a new ignition coil to be safe and try it out. But tech came back and said it failed. I asked if they could educate me a bit on how they test it and guy just said they run a "low rpm test, high rpm test, and bypass mode test"... And that it failed the low rpm test. So still not sure what that means, but the new one should be here by the end of the week for me to try.

I ordered a test light at the same time I ordered the replacement TFI module so can't put this back on and do the light test in the mean time but if a new one doesn't fix it then that'll be the next steps.

 

[RonD]

Thanks for the followup

 

[gaz]

dc,

The way I test for an intermittent low output coil is partly subjective but I have been lucky, even the way I learned it was an accident. Unplug a spark plug wire so that when you crank the engine, it shorts to the chassis; this needs to be done in the dark so that you can see the spark illuminate. If it is intermittent, it will be bright then not bright, also it will measure normal once or twice, then measure low on a multimeter.

 

[dcpppf]

Arg... New tfi in and no change. Plan to swap out the ignition coil to be safe tomorrow and if that doesn't do it use my new light tester to see what signals are going where.

Thought I had it figured out

 

[RonD]

The TFI system is autonomous, add 12v and ground and it works, no computer needed

Hall effect sensor in distributor provides the timing pulse, a 12volt on/off sensor as distributor shaft turns
TFI module grounds and ungrounds the coil based on that pulse
Coil builds up a charge when it has a ground from TFI, then discharges when its ungrounded

The test light(hooked to 12v) will show you if TFI is ungrounding the coil if test light is hooked to coil "-" wire, light goes off and then on

 

[Paulos]

Fast forward I do the plugs coil and dizzy with no change.

Did you replace the distributor or just the cap and rotor? The pickup coil is inside the distributor and could be the cause of the no spark problem. But your ignition and slow start problems are probably two different problems.

 

[dcpppf]

So I had done just cap and rotor on the dizzy.

So I replaced my already new ignition coil with a different new one and the truck is starting and running... But new oddity. Its like it has an occasional misfire every 5-10 seconds. Rpms will drop anywhere from couple hundred to a thousand and then bounce back up and idle smooth until it does it again. It even does it under load (aka me holding throttle open and revving at say 2500 rpm). Seems the miss is more frequent and much smaller (couple hundred rpm) when doing that vs idle.

I'll go back through all of the plug wires and make sure nothing got loose. If that doesn't fix it I suppose I can swap the old tfi module back on.

 

[dcpppf]

Ok final update and a few questions lol! I put the old tfi back in and all's right in the world again. Starts and idles just fine.

Questions...
1. Thoughts on what may have killed that ngk ignition coil prematurely? I only had a few hundred miles on it and less than 3 weeks.
2. Anyone have worries that the new delphi tfi cause those problems? Was like it just stopped firing the coil every so often. The real kicker was last time I started it up with the new tfi... The tach did two full 360s before settling around the 1200rpm Mark to idle lol. My fear is just that for some reason any other new tfi will cause the same problem years from now.

Appreciate everyone's insight and help! Sorry it ended up being something so stupid and simple lol

 

[RonD]

"new" means NEVER EVER tested now-a-days, not "it was tested and it works", unless it was a Motorcraft coil, they are tested

Ignition coils and spark modules run HOT, that's just part of doing a spark system
So they are higher failure rate parts
Newer designed coils are way better than the older designed ones but if new they are more likely to fail, sooner than later, but usually under warranty

The TFI module shouldn't Ground the Coil "-" with key on, that would cause it to heat up more, and could lead to early failure, you can test for that
The TFI should start grounding the coil only when distributor sensor starts to pulse

 

[dcpppf]

Thanks RonD! Good food for thought on my part. I suppose it makes sense that a "poor" coil would fail quickly like this one did; and definitely still under warranty. means I just need to drive the truck a bunch here these next few weeks again. I'm hoping to start the tie rods tonight and then will be piling more miles on.

As for the TFI right now I have no concerns/fears; just the fear that when this one goes that the next one will cause problems like that Delphi did for me. No sense in worrying about it now I suppose at least.